ASD is a common childhood disorder, which occurs in approximately 3.4 out of every 1,000 children, and requires a lifetime of care that leads to a significant burden for both families and state agencies. Core features of ASD include deficits in socialization, communication and behavior, and can present with other comorbidities such as intellectual disability, epilepsy, anxiety, depression, attention deficits and sleep disorders. The majority of ASD cases are complex and classified as sporadic, having a multitude of factors that combine to produce a disease phenotype; however, approximately 20% of ASD cases are syndromic with a well-established genetic cause. Despite the genetic heterogeneity between different types of syndromic ASD, these disorders display an incredible amount of phenotypic overlap. This overlap may indicate that the causal mutations across disorders, funnel through common molecular pathways during neuronal development, and thus indicate the potential for generalizable treatments. Currently, pharmacotherapies are severely lacking, as no effective pharmacological agents currently exist to treat core ASD symptoms. Therefore, further research into the neurobiology and underlying pathophysiology of ASD is required. In our grant, we propose to model ASD by developing cell and animal models in which the ASD risk gene transcription factor 4 (TCF4) is mutated. TCF4 is associated with a rare neurodevelopmental model called Pitt Hopkins Syndrome (PTHS) that displays autism features. We hope by modeling this disorder we can identify cellular and molecular mechanisms associated with risk for ASD that will eventually lead to the discovery of therapeutic interventions. In Aim 1, we demonstrate that Tcf4 regulates the development of oligodendrocytes (OLs) and mutations in Tcf4 result in hypomyelination. Our preliminary data from a mutant Tcf4 mouse model suggests that Tcf4 regulates the differentiation of oligodendrocyte precursor cells (OPCs) into mature OLs and this leads to a significant decrease in myelination. We propose experiments to identify cellular and molecular mechanism for how Tcf4 regulates OPC differentiation. In Aim 2, we propose experiments to connect Tcf4-dependent hypomyelination to physiological and behavioral deficits by specifically manipulating Tcf4 expression only in the OL-lineage. Moreover, we propose to rescue physiological and behavioral deficits by postnatally reinstating Tcf4 expression only in the OL-lineage to determine if this target rescue of myelination can lead to normalization of physiological and behavioral deficits. In Aim 3, we propose to use PTHS patient-derived induce pluripotent stem cells (IPSCs) to determine if OPC differentiation phenotypes observed in our mouse models translate into human models of disease. Together, these Aims are designed to identify therapeutic targets for the treatment of PTHS and potentially other ASDs.